It is well recognized by the consumer who has long been educated by banana importing companies that bananas should not be put in the refrigerator. Behind this admonition is the well recognized scientific fact that physiological changes take place in the underpeel of the banana as the temperature of the underpeel is lowered below 55.degree. F. As the temperature sinks lower the physiological changes are hastened until at temperatures, for instance between 45.degree. and 50.degree. F. the changes are rather quickly noticed by the eye of the observer as the rapid darkening of the underpeel takes place and this change in color shows through the exterior skin.
Those in the banana industry recognize that they must be very careful that bananas are not subjected to underpeel temperatures within the range of 45.degree. and 55.degree. F. if they wish the bananas to be a saleable commodity. Even with the care exercised in the banana industry it does occur on occasion that through inadvertence bananas are subjected to such chilling temperatures resulting in a total loss of the bananas.
To date, no method or technique is known to the prior art which would enable the banana to withstand such chilling temperatures within the range of 45.degree. and 55.degree. F. and accordingly greater care and vigilance is imposed. The solution to the basic problem has yet to be found.
It is important, to understand fully the present invention, to place the damage produced in the underpeel of the banana due to chilling temperatures of 45.degree.to 55.degree. F. in the proper perspective. The present invention is simply concerned with enabling the underpeel of the banana to resist the ravaging affects of these chilling temperatures and is not related in any manner to prior well known methods and techniques for preventing frost damage to fruits and vegetables. It must be made clear why the chilling damage to bananas is not common amongst other fruits and vegetables.
The banana is a substantially unique fruit due to the presence of the latex vessels which ironically are in the underpeel for the ostensible purpose of protecting the banana from foreign bodies and organisms upon breaching the integrity of the outer skin. The latex present in the latex vessels is designed to exude from any break in the exterior skin to prevent the entrance of any foreign body or organism through the break. The banana although a tropical product is at times subjected to chilling temperatures below 55.degree. F. from which follows the characteristic darkening.
It has now been discovered that these chilling temperatures also appear to bring about a phase change around the latex vessels in the underpeel. The phase change is found to occur in the cell membranes lining the latex vessels producing an increase in the permeability of these cell membranes for the liquid and solutes present in the cells surrounding latex vessels. The liquid and solutes from these cells then come into contact with the latex contained within the latex vessels and in a rather complex interreaction this latex darkens.
These changes are in contrast to those physical and chemical changes that take place when a fruit is frozen or subjected to heavy frost producing temperatures. Frost damage has been defined previously in the art as the U.S. Pat. No. 2,961,798 wherein it is maintained that the term designates damage due to sub-freezing temperatures, i.e., lower than 32.degree. F. Many fruits, vegetables including plants, leaves, stalks, buds, flowers and alike are adversely affected by such frost damage occurring only at temperatures lower than 32.degree. F. However, the banana underpeel is one of a very few parts of a plant that is rendered commercially useless at range 45 .degree. to 55.degree. F. This distinctive characteristic of the banana is contrasted by the fact that many plants at these temperatures particularly fruits and vegetables are purposely maintained to achieve a longer storage life.
The banana being a very temperature sensitive fruit, it is clear that there is no purpose whatever in attempting to protect it from frost damage. The simple reason is that long before the banana has been subjected to frost damage the underpeel would have been irreparably damaged by the chilling temperatures of 45.degree. to 55.degree. F. The illogic of applying any of the frost damage prevention techniques to bananas must therefore be manifest. The banana would be useless before any frost protection means was operable.
The prior art is limited to the use of oils and waxes including silicone oil for the purpose of preventing frost damage usually on living plants and their products. Generally the frost damage protection techniques relate to citrus trees which grow in the southern part of the United States and which may be subjected to occasional frosts. Bananas, indigenous only to a very few countries throughout the world, pose a completely different problem due to the unique presence of latex vessels and their great sensitivity to chilling at higher temperatures.
Many of the prior art patents relating to frost damage disclose various oils and waxes most of which, such as parafin wax, would be totally useless when applied to the banana due to the total failure to penetrate to the latex vessels.
No prior art treatment for temperature damage in any range is known. Toulmin U.S. Pat. No. 2,995,538 however, does disclose a treatment for bananas which provides a flexible and tough coating to prevent deterioration and injury due to mechanical abrasion. This protective coating is external only and utilizes specific siloxane resins that would be incapable of penetrating into the underpeel at the sites of the latex vessels. To achieve the abrasion protective coating this patented disclosure would necessarily require a coating that would cover and remain on the exterior skin rather than penetrate through and into the underpeel.